The present invention relates to a device for controlling the positioning of the cursor displayed on the screen of personal computers, workstations, video terminals and generally of interactive systems that dialogue with the operator by means of images, either artificially generated or taken from reality.
As is known, a cursor is positioned by the operator in order to point at items of the displayed images, select them, engage them and cause the displaying system to move them, et cetera.
Cursor control is performed by virtue of devices which are generally termed "pointing devices", such as a mouse, a trackball, a joystick, and the like.
Existing pointing devices generally convert the movements of an actuation element controlled by the operator (in the case of the mouse, the body itself of the device) into signals used to control the proportional movements of the cursor on the screen.
A low or high proportionality factor is matched by a respectively low or high sensitivity of the control chain; sensitivity can also vary dynamically.
This arrangement has some intrinsic disadvantages:
a) if sensitivity is low, considerable space must be devoted to the pointing device: for example, the smooth and uncluttered worktable surface required to make a mouse run. Devices that require such space cannot be integrated with a keyboard and can be awkward in use due to the extent of the movements that they require (both to operate them and to move one's hand between said devices and the associated keyboards).
b) If sensitivity is high, the natural difficulty of controlling very small hand movements arises. For example, it becomes easy to induce unwanted movements of the cursor due to trembling or small involuntary movements of the hand.
Often it is not possible to find a compromise that avoids both drawbacks even by providing dynamically variable sensitivity.
The measurement of significant movements furthermore entails, in many pointing devices, the presence of moving parts that make them subject to wear, to the need for maintenance, and to limitations in reliability.
In order to overcome these problems, static pointing devices, such as the one proposed in European publication no. 433205 filed by International Business Machines Corporation, Armonk (USA), have been introduced. This device is integrated in the keyboard of a computer and controls cursor movements through the application of forces to an actuation button; the components of the force that are tangent to the plane of the keyboard determine the direction of the movements, and the component of the force that lies at right angles to the plane of the keyboard determines the speed of said movements.
Static-type actuation elements, such as the one described in European publication no. 433205, can solve the above described problems, ensuring compact size, optimum sensitivity and lack of mechanical wear. However, they are characterized by intrinsic difficulty in adjusting the action that is applied. It is in fact known that a human operator is not very accurate in assessing and controlling the amount of force applied to a fixed object. Without adequate tactile feedback, the only accurate reaction on which the operator of a static pointing device can rely to adjust his action is therefore the visual reaction provided by the movements of the cursor themselves; however, these movements occur in practice with small variable delays, and this causes the need for subsequent corrections to cancel the excess actuations. Furthermore, applying to key forces that are tangent to the keyboard surface is ergonomically unnatural, since it is dissonant with respect to the actions to be performed, even simultaneously, on the other keys, including the clicking keys themselves which are associated with the pointing device to control the execution of operations on the items pointed at with the cursor. Other devices that use similar principles and are at least partially subjected to similar ergonomic limitations are described in publications WO-A-8906023 (NCR Corp.) and DE-A-3523270 (Siemens AG).